A conventional method for crystal growth of a GaN semiconductor material to give a thick film generally comprises forming a buffer layer of ZnO and the like on a sapphire substrate and growing a GaN semiconductor material by an HVPE method. An improved technique thereof involves the use of a substrate such as one made from spinel, LGO, LAO, ZnO, SiC and the like or a substrate showing easy cleavage performance, instead of the sapphire substrate.
However, the crystal growth of a GaN semiconductor material to give a thick film results in tremendous amounts of stress applied on the interface between GaN and sapphire substrate due to different lattice constants and coefficients of thermal expansion, which in turn leads to a problem in that GaN is broken and a bulky substrate cannot be obtained. In addition, this method produces only a substrate having an extremely great dislocation density (e.g., 1.times.10.sup.9 cm.sup.-2 -1.times.10.sup.10 cm.sup.-2). By dislocation is meant here a defect that occurs when a semiconductor layer is grown on a substrate under a lattice mismatch. The dislocation thus created advances upward along with the growth of the crystal layer and passes through an active layer to form a continuous defective portion called a dislocation line (continuous dislocation). Inasmuch as this dislocation is a crystal defect, it acts as a non-radiative recombination center or as a path of a current to ultimately induce current leakage when such GaN semiconductor material is used for a light emitting element, which in turn degrades light emitting performance and shortens the service life.
It is therefore an object of the present invention to provide a GaN group crystal base member having a low dislocation density.
Another object of the present invention is to provide use of the aforementioned GaN group crystal base member.
Yet another object of the present invention is to provide a method for producing the aforementioned GaN group crystal base member and a method for producing a light emitting element which is one use thereof.